1. Field of the Invention
The invention pertains to a left-handed substance as well as to a wave-guide device and an antenna incorporating this left-handed substance. An object of the invention is also a method for manufacturing this left-handed substance.
Here below in the description, unless otherwise stated, the terms “permittivity ∈” and “permeability μ” when used without any other specific information refer to relative permittivity and relative permeability.
Left-handed substances were presented for the first time by Victor Veselago in:
“The Electrodynamics of Substances with Simultaneously Negative Values of ∈ and μ”, Soviet Physics USPEKHI, vol. 10, n° 4, January-February 1968”.
These materials have the property of simultaneously presenting negative permittivity ∈ and negative permeability μ within a given range of frequencies. These left-handed substances have many atypical properties, such as:                a negative refraction index,        the trihedron formed by the vectors E (electrical field), H (magnetic field) and k (direction of propagation of the waves) is inverted (the term used is “reversed”) as compared with materials with positive (the term used in this case is “forward”) permittivity and permeability,        the phase speed and the group speed have opposite signs,        the Doppler effect is inverted,        etc.        
2. Description of the Prior Art
Because of these atypical properties, these left-handed substances may find numerous applications, especially in the processing of the electromagnetic waves.
It has been proposed especially to use these left-handed substances in wave guides, filters, or antennas. For such applications, it is desirable that the frequency band in which ∈ and μ are simultaneously negative should in the hyper-frequency domain, i.e. between 1 and 60 GHz.
Various research projects have been conducted to achieve this result. For example, a substance having these properties is described in the following document D1:    D. R. Smith, W. J. Padilla, D. C. Vier, S. C. Nemat-Nasser, and S. Schultz, “Composite Medium with Simultaneously Negative Permeability and Permittivity”, Phys. Rev. Lett., Vol 84, N° 18, p. 4184, 2000.
These known substances are often called “metamaterials”. They comprise a heterogeneous material formed by an array of conductive wires positioned relative to one another in such a way as to present a negative ∈ relative to the electromagnetic waves which have an electrical field parallel to the biggest dimension of these wires and are propagated at a frequency below the electrical plasma frequency of the substance.
The electrical plasma frequency as well as the sizing of this array of conductive wires to obtain a value of ∈ below zero has been described especially in the following document D2:    J. B. Pendry, A. J. Holden, W. J. Stewart, and I. Youngs, “Extremely Low Frequency Plasmons in Metallic Mesostructures”, Phys. Rev. Lett., Vol. 76, N° 25, 1996.
Broadly speaking, the electrical plasma frequency of the substance is the value of the frequency of the incident electromagnetic wave for which the real part of ∈ gets cancelled out.
These prior-art substances generally comprise another heterogeneous material formed by another array of conductive patterns that are laid out relatively to one another so as to present a negative value of μ in the desired frequency band. Typically, this other array is a array of conductive split rings (also known as Pendry rings) used to artificially generate a negative μ value through an electromagnetic resonance phenomenon LC in a range of frequencies situated immediately after the magnetic plasma resonance frequency. Broadly speaking, the magnetic plasma resonance frequency is the value of the frequency of the incident electromagnetic wave for which the real part of μ gets cancelled out. Such arrays can be used to obtain a negative μ value after the magnetic plasma resonance frequency. These arrays are for example examined in the following document D3:    J. B. Pendry, A. J. Holden, D. J. Robbins, and W. J. Stewart, “Magnetism from conductors and enhanced nonlinear phenomena”, IEEE Trans. MTT, Vol. 47, N° 11, 1999.
The above two arrays are laid out so as to present both a negative ∈ value and a negative μ value.
The arrays described here above consist of an elementary pattern called an “elementary cell” repeated at regular intervals in one or more repetition directions. The regular interval is called the “pitch” of the array.
The size of the elementary cell in the direction of repetition is chosen in such a way that the substance behaves like a homogeneous material with respect to the wave illuminating this substance with a frequency included in the range of frequencies for which the values of ∈ and μ are simultaneously negative. To this end, the size of an elementary cell is chosen to be smaller than and preferably several times smaller than the wavelength of the illuminating wave and typically ten times smaller. At the same time, the pitch of the array is far greater than 1 micrometer so that, at a microscopic scale, the layout of the wires relative to one another can be clearly discerned.
These prior-art substances have several drawbacks:                the frequency band in which ∈ and μ are simultaneously negative is narrow (i.e. it is at most a few hundred Megahertz)        the amplitude of the absolute value of μ in this frequency band is low (i.e. it is smaller than a few units)        
Furthermore, the sizing and tunability of the array that make it possible to obtain a negative μ are limited. Indeed, to obtain a negative μ for a given working frequency, it is necessary to build an array having a magnetic plasma resonance frequency neighboring this working frequency. To this end, the dimensions of the split rings must be matched with the wavelength of the working frequency. Now the modification of the size of the split rings cannot be done dynamically, thus preventing the tuning of these metamaterials at a given working frequency after it has been manufactured. Even if the working frequency is known before the manufacturing of the array, the dimensions of the split ring needed to work at this frequency may be impossible to achieve either because they are too small or because on the contrary they are far too great.
It is therefore not easy to use the known substances combining two heterogeneous materials to obtain negative values of ∈ and μ simultaneously, in physical applications.
Recently, it has been proposed to use only one array of conductive wires arranged in relation to one another so as to present negative permittivity to electromagnetic waves having an electrical field parallel to the greatest dimension of these wires and being propagated at a frequency below the electrical plasma frequency of the substance, each wire being made out of a conductive magnetic material having negative permeability for a range of frequencies of the electromagnetic waves below the electrical plasma frequency of the substance and when there is no external artificial static magnetic field. The wires have a circular cross-section whose diameter is greater than 1 μm.
For example, a substance of this kind is described in the following document D4:    H. García-Miquel, 1,a_ J. Carbonell,2 V. E. Boria,2 and J. Sánchez-Dehesa1, <<Experimental evidence of left-handed transmission through arrays of ferromagnetic microwires>>, APPLIED PHYSICS LETTERS 94, 054103—2009—
In this last embodiment, it is not necessary to plan for another structure in addition to the array of wires, for example an array of split rings, so that this substance will show left-handed properties in a range of frequencies. The structure of this left-handed substance is therefore simpler than that of substances using two heterogeneous materials and especially metamaterials. Indeed, this substance uses the natural ferromagnetic resonance frequency of the material used to form the conductive wires. This ferromagnetic resonance frequency is qualified as being natural because it exists in the absence of any external static magnetic field. The term “static magnetic field” designates a direct magnetic field and not an alternating magnetic field.
Furthermore, the positioning of the ferromagnetic resonance frequency in the neighborhood of the desired working frequency does not call for modifying the pitch or dimensions of the elementary cell of the wireless network. Here, it is sufficient to play on the choice of the conductive ferromagnetic material used to make the wires, i.e. for example, on an external static magnetic field. Given that it is not necessary to adapt the dimensions of the array to bring about a variation in the frequency of the ferromagnetic resonance of this substance, the sizing and tunability of this substance are simplified.
However, in practice, as illustrated by the experimental results shown in the document D4, this material has solely left-handed properties if it placed in an external static magnetic field. This is one particularly major drawback for the use of this type of left-handed substance.